Module 3 - Neuromechanics Flashcards
Central nervous system (CNS)
Brain + spinal cord protected by boney structures
Peripheral nervous system (PNS)
- Nerves outside the CNS
- Somatic component includes sensory (senses) + motor (movement, muscle cells) nerves
Autonomic nervous system (ANS)
- Control system of body functions such as breathing, cardiovascular function, etc.
- Sympathetic + parasympathetic
Components of brain
- Cerebrum (bulk of grey matter, neuron cell bodies)
- Diencephalon
- Cerebellum
- Brain stem
Cerebrum (components + function)
- Cerebral cortex
- Hippocampus + amygdala (long-term memory)
Diencephalon (components + function)
- Thalamus (sensory)
- Hypothalamus (homeostasis)
Brain stem (components + function)
- Midbrain
- Pons
- Medulla (cardiovascular function)
Spinal cord
Runs through vertebra, connects to peripheral on the sides of each vertebra
Grey matter
- Cell bodies, dendrites, axon terminals
- Areas of synaptic connections
White matter
- Axons
- Pathways between grey matter areas
Spinal cord to PNS
Grey + white matter of spinal cord –> ventral + dorsal roots (projections coming out of vertebra) –> go on to form PNS
Peripheral nerves
- Nerve –> collection of many neurons (cells)
- Motor nerves: efferent neurons –> control effectors such as skeletal muscles
- Sensory nerves: afferent neurons –> detect stimuli + relay that info to CNS
Neurons
- Basic information processing unit: receives input, process info, + provides output
- Neurons are excitable cells; send/stop action potential
- In a balancing act (tug-of-war) between “turn on” (depolarize + receive info from other neurons) + “turn off” (stay at -70mV)
Neuron anatomy
- Processing section: nucleus, soma (cell body), dendrites (receive info from other neurons)
- Communication section: axon (where AP transmitted, can be very long), axon terminal (where synapses form w/ other neurons)
Axon hillock
- Where processing section connects to communication section (via axon)
- Decides if AP is transferred to axon (is there enough AP?)
Membrane potential
- Negative at rest (-70mV)
- Depolarization = membrane potential becomes +ve (+20mV) (once AP surpasses thershold)
- Repolarization/hyperpolarization = membrane potential becomes negative (-70mV)
- Has a refractory period (opening/closing of ion channels) –> then resting state
Glial cells
Provide support to neuron function (helps with structure, metabolism, + repair) (helper/support cells)
Synapse
- Structure permitting communication b/w 2 neurons
- Where neuron interacts w/ another neuron/cell type
Action potential
Change in electrical potential that can travel along a cell membrane (-ve to +ve –> depolarization)
Neurotransmitter
A chemical messenger that transmits a message b/w cells
Cell to cell communication
- Action potential travelling down an axon is an electrical signal
- This electrical signal converted to chemical signal at axon terminals
- Chemical signal converted to electrical signal at post-synaptic neuron
Measuring the nervous system
- Structure: structural imaging –> MRI
- Function: neuronal activity –> functional imaging, electroencephalography (EEG) –> measures electrical activity of brain, electrophysiology
- Behaviour: times (e.g. reaction time), non-timed (errors, response)
Biopotential
- Electrical potential measured between 2 points in living cells, tissues, and organisms (electrical diff. b/w 2 points) –> e.g. neurons, skeletal muscles
- Electrodes, amplifiers, + electrical activity
- EMG, ECG, EEG
Electroencephalography (EEG)
- Measuring electrical activity (biopotentials) arising from the CNS
- What is being measured? –> neuronal activity –> APs (de/repolarization)
Muscle
- Tissue made up of many muscle cells + associated connective tissue
- 3 main types: skeletal, cardiac, smooth
Skeletal muscle cell
- Muscle fibre/myocyte –> individual cell that when activated produced force that can lead to motion
Sarcomere
Fundamental unit of skeletal + cardiac muscle. MANY sarcomeres arranged in sequence within single myofibril + many myofibrils make up a muscle cell
Myofilaments
Sarcomeres are composed of highly organized arrangement of myofilaments (composed mainly of actin + myosin) that interact w/ each other to generate force (slide across each other)
Skeletal muscle structure (levels of organization)
- Full, highly organized, full of machinery used to generate force (proteins, structures, etc.)
- Fascicle: unit of a muscle cell
- Muscle fibre: unit of a fascicle
- Myofibril: unit of a muscle fibre (long strands of sarcomere)
- Sarcomere: unit of myofibril (ends are Z-lines)
- Sarcolemma: cell membrane
Cross bridge
- Binding of actin to myosin myofilaments + change in confirmation of myosin
- Cross bridge cycle: process involving attachment, conformation change + detachment (with ATP) that generates force
Sliding filament theory
Theory explaining mechanism of muscle contraction associated with cross bridge cycling + sliding of myofilaments past each other to generate force
Cross bridge cycle overview
- Sarcomere shortens when myosin heads in thick myofilaments form cross bridges w/ actin in thin filament
- Formation of cross bridge –> initiated when Ca2+ released from sarcoplasmic reticulum bind to troponin –> changes shape
- Tropomyosin moves away from myosin binding site on actin –> myosin head binds to actin + forms cross bridge (myosin head must also be activated before cycle can begin –> ATP hydrolysis provides energy to activate into cocked position)
- Ends when Ca2+ is actively transported back to SR, troponin returns to original shape –> tropomyosin covers myosin binding site on actin
Cross bridge cycle steps
1) Cross bridge formation: myosin head binds to actin, inorganic P released, bond is stronger
2) Power stroke: ADP released + activated myosin head pivots, sliding thing myofilament toward centre of sarcomere
3) Cross bridge detachment: another ATP binds to myosin head –> link b/w myosin head + actin weakens –> myosin head detaches
4) Reactivation of myosin head: ATP hydrolyzed –> energy reactivates myosin head –> cocked position
As long as actin binding sites exposed –> cross bridge cycle repeats –> thin myofilaments pulled towards each other –> sarcomere shortens
Motor neuron
Neuron that synapses w/ skeletal muscle cells
Motor unit
Motor neuron + ALL muscle cells it innervates (neuron interacts w/ diff. cell type) –> 100s-1,000s-100,000s
Neuromuscular junction
Synapse b/w motor neuron + a skeletal muscle cell
Muscle action potential
Action potential (depolarization –> repolarization on membrane of skeletal muscle cell)
Neuromuscular activation
- Electrical: depolarization of motor neuron (neuronal AP)
- Chemical: neurotransmitter (acetylcholine (ACH)) release at neuromuscular junction
- Electrical: depolarization of muscle fibre
- Mechanical: cross-bridge formation + sarcomere shortening
How can you control the amount of force a whole muscle generates?
- Muscle fibres activate in an ALL or NONE manner (1 motor neuron –> all muscle cells it innervates/AP arrives at one muscle –> ACH released –> muscle contracts)
1) Motor unit recruitment
2) AP frequency
In general: increase in AP frequency –> increase in force
What determine the maximum isometric force a whole muscle cell could generate (assume maximal potential frequency and recruitment + optimal length)?
- Bigger muscle –> more sarcomere –> more force
- Cross-sectional area of a muscle –> more muscle cells –> more sarcomeres –> more cross bridges –> more force
Electromyography (EMG)
Technique to measure electrical activity produced by muscles (muscle APs) that occurs when muscle is stimulated
Surface EMG
- Skin prep + electrode placement –> very important
- Need to know direction of muscle fibres
- Pro: relatively easy technique, less risk of damage/infection
- Con: limited to superficial muscle, unsure of which muscle is producing electrical activity (risk of interference)
Intramuscular EMG
- Small needle is inserted into a muscle + electrical activity is recorded directly
- Pro: specific choice of muscle
- Con: invasive (skilled technician needed)
Axes of EMG graph
- y-axis: mV, V
- x-axis: time
Relationship b/w EMG amplitude + muscle force
- Positive relationship b/w RAW (unfiltered, no mathematical manipulation) EMG + muscle force
- As EMG increases, force increases
- CANNOT compare RAW EMG b/w diff. muscles (e.g. diff. size) OR b/w people
- Slight delay/lag time w/ force production compared to EMG
Stimulus response
- Series of events that req. afferent info + involve some sort of efferent response/effect
- Stimulus presented –> SENSORY: info going to CNS through afferent neurons –> CORTICAL: neural info is processed (combined with prior behavioural instructions) –> MOTOR: an effect is determined + is transported through efferent neurons –> muscles activated to perform task
- ALL steps take time (short time)
Reaction time
- Time it takes CNS to sense, process, + initiate response to stimulus (from stimulus to onset of response)
- Afferent –> processing –> efferent
Movement time
- Time it takes person to execute specific movement (does not include reaction time)
- Time from onset muscle activation (EMG) to end of response
- From muscle activated (start) to end of response
Response time
- Reaction time + movement time
- Total time from stimulus detection –> end of stimulus response
What factors is reaction time dependent on?
Stimulus intensity + modality (type)
- Cognitive/neural impairment
- Age
- Presence/absence of neurological disease + inheritence
- Medications/drugs
- Environment (distractions)
- Sex
SRT: simple reaction time
CRT: choice reaction time
Simple reaction time (SRT)
- Only 1 stimulus + 1 response
- e.g. “Hear something –> push a button”
Choice reaction time (CRT)
- Number of diff. stimuli presented each required diff. response
- Reaction time gets longer w/ more stimuli
- e.g. various pitch sounds –> press diff. button for each
Dual-task interference
- Simultaneous performance of 2 tasks often leads to performance deficits in component tasks
- Thought to be proof of capacity limitation in cognition
- Can’t to Z things at the same time as fast is if they were separate
Multi-tasking:
- Possible, some people better than others
- Aspect of learning + practice
Agonist
Muscle primarily responsible for a movement (e.g. biceps brachii in bicep curl)
Antagonist
Muscle that opposes the movement of agonist (e.g. triceps brachii in bicep curl)
Agonist + antagonist dependency
- Dependent on posture + movement
- e.g. Knee flexion + extension while sitting vs lying down
- Gravity always affects body –> posture + movement change agonist vs antagonist
Reciprocal contraction (/activation) + benfits
- Simultaneous activation of agonist + inactivation (relaxation) of antagonist
- Maximizes amount of force it can produce (does not need to overcome agonist)
Co-contraction + benefits
- Simultaneous activation of agonist + antagonist
- Stabilizes joint
- e.g. Carrying heavy load –> stability of joint needed to support weight + prevent injury
Graphing joint kinematics + EMG
CANNOT graph without kinematics (EMG only) –> don’t know what’s going on
Biomechanics
Study of effects + control of forces that act on + are produced by living beings
Kinematics
Study of MOTION of objects (w/out reference to the FORCES that caused the motion)
Kinetics
Study of FORCES that cause motion
Linear kinematics terms
- Displacement (m)
- Velocity (m/s)
- Acceleration (m/s^2)
Angular kinematics terms
ROTATIONAL
- Angular displacement (rad)
- Angular velocity (rad/s)
- Angular acceleration (rad/s^2)
Force
LINEAR
- Action/influence that moves body or influences movement of the body
- UNIT: newtons (N)
- Internal forces: created primarily by skeletal muscles
- External forces: created by ground (ground reaction force), external loads, other individuals, + from passive sources (e.g. wind resistance)
Moment
ANGULAR
- “Moment of force”
- Force that tends to change the rotational motion of an object
- UNIT: Nxm
- M +ve: counter-clockwise
- M -ve: clockwise
Vectors
- Have magnitude (length) + direction
- Tail and head
- A non vertical/horizontal vector is a sum of its vertical + horizontal components
Moment arm
- Perpendicular distance from application of force
- Distance b/w point of rotation + application of force
- Larger moment arm –> larger moment of force (rotational)
Centre of mass (COM)
Point in centre of object where all of the mass of object is equally distributed in all directions
Centre of mass (COM) and gravity
Force of gravity acts in downward direction (-y) through the centre of mass (COM) of an object
Force of gravity
- Mass x acceleration due to gravity (9.8m/s^2)
F = m x a
F = 5kg x -9.8m/s^2
F = -49N
Moment calculation
M = F x d
Approach 1:
- F = force applied
- d (moment arm) = perpendicular distance b/w axis of rotation + line of force
- No 90 degree angle –> trig
Approach 2:
- F = force vector component that is perpendicular to segment
- d (moment arm) = distance from axis of rotation to point of application of force
- USING THIS ONE
Muscle force and moments
- Must consider all moments acting on a segment –> must consider the sum of the moments
- If a segment is stationary –> sum of M = 0
Kinematics measurement
- Visual observation
- Goniometer (instrument to measure angles): hand held/electronic
- Inertial sensors: measure acceleration
- Optical/magnet motion capture: gold standard for measuring kinematics
Goniometer types + pros/cons
Hand held:
- Pro: can do everywhere on anyone
- Con: guess, estimate, not very accurate, stuck with static
Electronic:
- Pro: mobile
- Con: may not be as accurate
Potentiometer:
- Pro: accurate joint angle
- Con: tethered to one spot, immobile
Inertial sensors pros/cons
High-end:
- Pro: accurate
- Con: expensive
Personal (e.g. Apple Watch):
- Pro: affordable in comparison, easy to use
- Con: not as accurate
Optical motion capture
- Gold standard (one of best techniques, go-to, reliable) of measuring kinematics
- Cameras tracking dots: know exactly where each joint is in 3D (inertia + joint angle), can calc. displacement, velocity, acceleration, etc.
- Pro: really accurate/gold standard
- Con: expensive, software + trained people required
Kinetics measurement
- Manual assessment
- Dynamometer: device to measure force, moment, or power (hand held/electronic)
- Force plates: instrument to measure ground reaction forces
Manual muscle testing pros/cons
- Want to understand where deficits in body are through comparison w/ healthy parts
- Pro: can do it anywhere
- Con: lots of training required, not very accurate (subjective, don’t know how many N)
Dynamometer types + pros/cons
Hand held, hand grip:
- Pro: objective (N, kg), measures amount of force
- Con: have to be able to brace yourself to oppose the force
Isokinetic dynamometer:
- Pro: can test most joints, can control many variables (joint angle, speed (fixed/variable), resistance), completely adjustable, 360 degree rotation
- Con: Expensive
Force plates
- Gold standard in measuring kinetics (forces)
- Can get a sense of interaction w/ environment while doing things
- Need kinematics to go with kinetics for full picture
- Pro: can measure force in all 6 directions + moments, really accurate
- Con: alone –> no idea of kinematics, really sensitive, some are anchored into ground/others mobile
What is included in the foundation of biomechanical research?
- EMG (muscle activation)
- Kinematics (movement)
- Kinetics (forces)
Combined = full picture
Gold standards of biomechanics
- Optical motion capture: kinematics
- Force plates: kinetics
